Loop antenna



Feb. 14, 1939. G. M. -cHARRu-:R

' LOOP ANTENNA Filed Maron 17, 195s Patented UNITED STATES'PATENT OFFICELOOPANTENNA George M. Charrier, Oaklyn, N. J., assigner to My inventionrelates to loop antennas.

Radio Corporation of Delaware America, a corporation of ApplicationMarch17, 1936, Serial No. 69,265

2 Claims.

More

particularly my invention is directed to a shielded loop antenna of lowcapacity andvto a method of winding same.

Loop antennas have been primarily used in direction finding. It has beenfound desirable to shield such antennas to avoid capacity pickup.

While shielding reduces the undesired capacity pickup, it has the veryundesirable effect of increasing the capacity of the loop winding to thegrounded shield.

One of the objects of my invention is to shield a loop antenna withoutdeleteriously increasing the capacity of the loop winding. Anotherobject is to provide means for winding a loop within an annular channelin a shield. A further object is found in the novel method of windingthe loop inductor.

An additional object is to form a mid-tapped loop antenna inductor whosehalves will be balanced capacitively with respect to ground.

My invention may be best understood by reference to the accompanyingdrawing in which Figure I represents an elevational view of oneembodiment of my invention,

Figure II is a plan view of the loop antenna Of Figure I,

Figure III is an enlarged viewv of a slip ring assembly which isconnected to the loop, and

Figure IV is lan enlarged sectional View taken along the lines IVe-IV ofFigure I.

The loop inductor I is composed of a strip of exible insulating material3 which has been secured in circular form by cementing, riveting orotherwise fastening the ends 5, 1. A plurality of turns of suitablyinsulated wire 9 are wound on the circular form. The method of windingand securing the wire will be hereinafter described.

VA metallic shield I I surrounds the loop inductor I. The shield ispreferably of hollow circular cross section; it may be streamlined foraircraft or the like.

The internal diameter of thehollow tween these ends may be covered by apiece of in- K sulating material such as a rubber tube I1.

The base of the shield member II is clamped between a pair of elementsI9, 2l.

A pair of screws 23, 25 clamp the slip ring assembly21 of Figure III tothe lower element,2I-.

The slip ring assembly 21 is made by suitably embedding a pair of sliprings 29-3I within an insulated member 33.

This insulated member, including (Cl. Z50-33) the slip rings, isinserted within the slip ring assembly as shown. A pair of brush members35, 31, bearingfon the slip rings, are supportedn the lower base member39. The entire loop assembly is rotatively mounted on the lower base bya shaft 49 which is secured to the loop assembly. A collar 4I preventsupward movement of the loop assembly.

The loop may be rotated by a handle 43, or other suitable means. Thelower base 39 is mounted on any convenient support. The inductor leads45, 41 are connected to the brushes 35, 31. It should be understood thata connection' intermediate the ends of the loop may be brought outthrough a third slip ring conductor. Since the terminal apparatus is notpart of the present invention, it is not necessary to describe suchapparatus which is well known to those skilled in the art. Y

Iv prefer to iirst form the annular shaped shield II from a non-ferrouspipe of aluminum, brass, copper, or the like. The insulated tubing I1 istted over the pipe but in a position exposing the pipe ends I3, I5. Astrip 3 of flexible insulation material such as Bakelite, or fibre iscut to a width slightly less than the diameter of theY annular channelwithin the. shield. This strip is threaded through the annular channelas shown. The ends of the strip are secured by small rivets or cement.The strip is self-supporting because it just ts the channel as shown inFigure IV. The slight clearance permits rotation of the strip within thechannel.

The inductor is formed by cementing or otherwise securing one end of anappropriate length of insulated wire to the insulated strip. The stripis then manually rotated within and with respect to the annular channel.Since the wire has been attached to the strip each rotation of the stripwill cause one turn to be wound on the strip. It is preferable tosecurel each quarter turn of wire to the strip by a quick drying cement.It should be apparent that each turn of the strip with respect to theshield applies a turn of wire to the inductor. The required number ofturns may be wound in a single layer with each turn spaced from theadjoining turn, or the inductor may be bank wound. The terminals 49, 5Iof the inductor winding are brought through appropriate apertures to theslip rings 29, 3|.

. After the winding has been completed and the terminalshave beenanchored and connected, no further supports or fittings are required tolocate the inductor within the shield. The capacity between the turnsand the shield is a minimum because of the natural and maximum spacingof the elements. The rubber tubing I'I is slipped around the shielduntil it covers the space between the ends I3, I5. The tubing may thenbe cemented in position. It is customary to ground the shield. The endsI3, I5 should not be conductively joined to avoid the short circuitingeffect which a closed shielding ring would have on the loop inductor.

A shielded low capacity loop antenna has been described. The inductorsupporting strip is located Within an annular channel in the shield andis supported thereby. In this position the capacity from the inductorwindings to the shield is a minimum, The symmetrical arrangement of theinductor with respect to the shield provides a capacity balance betweenthe halves of the loop if a mid tapped inductorv is desired. The methodof winding the inductor within the annular channel has been described. Ido not limit my invention to the precise showing as numerousmodicationswithin its scope. are possible; for example, the insulated support maybe an edgewise formed circular strip of Bakelite.

I claim as my invention:

1. A loop antenna including arformed metallic tube of annular shapehaving an open section between the ends of said tube, a exible insulatedform, said form being of hollow cylindrical shape and supported withinsaid tube at approximately the maximum cross-sectional diameter, aninductor comprising a plurality of turns of conductor mounted on saidform so that each turn of said inductor has an inductance substantiallyequal to that of every other turn and so that the corresponding turnsoneither side of the center form substantially equal capacities Ito groundand to every other turn, means for securing said turns to said form,insulated means for covering said open section, a member for clamping'and supporting said tube, a second member forming a face for said rstmember and slip rings for connecting said inductor to electrical membersin said second member.

2. In a loop antenna of the character of claim 1 means operativelyconnected to said loop for rotating said loop and irst member on saidsecond member.

. GEORGE M. CHARRIER.

